Ultraviolet radiation and blue light blocking polarizing lens

ABSTRACT

A lens (10) that substantially blocks horizontally polarized light and selectively blocks wavelengths between 300 and 549 nanometers. The selective blocking is controlled by a sharp cut-on filter (14) selected to cut-on at either 450, 500, 515, 530, or 550 nanometers. The specific blocking and cut-on point selected is dependent upon the ultimate usage/environment of the lens (10). If a 450 cut-on filter is selected, wavelengths between 300 and 449 nanometers are blocked before a cut-on occurs at 450 nanometers; similarly, a 550 cut-on filter blocks wavelengths between 300 and 549 nanometers before a cut-on occurs at 550 nanometers. The lens (10) also allows 30 to 40 percent of wavelengths over 625 nanometers to be transmitted. The filter (14) in combination with the polarizer (16) blocks harmful Ultraviolet radiation and blue light. While a beneficial and calming effect is achieved by wearing only blue-blocking lenses, the addition of the polarizer (16) substantially enhances the calming effect and the improvement of vision without visual discomfort.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.07/019,556 filed Feb. 26, 1987 now abandoned.

TECHNICAL FIELD

The invention pertains to the general field of sunglass lenses and moreparticularly with lenses that combine a polarizer that blockshorizontally polarized light and a sharp cut-on filter that blocks bluelight and ultraviolet radiation.

BACKGROUND ART

It is well known that energy radiated in the form of light is capable ofinducing and/or promoting certain photochemical reactions and thatdifferent photochemical reactions are induced by the action of lightrays (or photons) of various wavelengths. Certain wavelengths of light,especially those in the blue and ultraviolet range, are known to beinjurious to the eye.

Dyed lenses, when used with prescription or non-prescription sunglassesare basically intended to fulfill one of two functions: the firstfunction is either selective or overall reduction of the injurious lightand radiation. Lenses dyed for this purpose are known as protectivelenses. Protective lenses may block harmful wavelengths either byreflection or, more commonly, by absorption. The second function isfulfilled by lenses which fulfill cosmetic requirements and are referredto as fashion tints. Combination dyes covering both requirements arealso available.

In the current art, there are protective lenses that block blue andultraviolet wavelengths and there are separate polarizing lenses thatblock horizontally polarized incident light. The combination of apolarizing and a blue and ultraviolet blocking lens is not currentlyavailable as confirmed by a listing of lenses published in 1986 byRetinitis Pigmentosa International and a search of the advertisingliterature. The non-availability of these combination lenses is due, inpart, to the little research that has been conducted by sunglasscompanies on the detrimental effect of the blue light hazard to theretina of the eye and the technical problems encountered in combiningthe temperature-sensitive polarizing film with the dye. This problem hasbeen solved by the instant invention by selecting dyes that can providethe required blue blocking at a temperature that will maintain theusefulness and structural integrity of the polarizing film.

A search of the prior art did not disclose any patents that readdirectly on the claims of the instant invention. However, the followingU.S. and foreign patents were considered related:

    ______________________________________                                        PATENT NO.   INVENTOR      ISSUED                                             ______________________________________                                        4,261,656    Shy-Hsien Wu  14 April 1981                                      2,307,602 (DE)                                                                             Krumeich      29 August 1973                                     3,588,216    Bloom         28 June 1971                                       3,460,960    Francel et al 12 August 1969                                     2,643,982    Riley         30 June 1953                                       ______________________________________                                    

The Shy-Hsien Wu patent discloses a transparent, optically clear articlethat consists of a glass or plastic base element that supports a thinand delicate organic or inorganic surface film such as a plasticpolarizing film. The film is protected from the damaging effects ofmoisture, scratching and abrasion by a protective plastic coating. Thehardness of the protective coating is controlled to avoid excessiveflexibility or brittleness, so that good scratch resistance over arelatively soft film is obtained.

The Krumeich German Offenlegungsschrift discloses an optical filter thatcorrects red/green color blindness. The filter is designed so that inthe blue to green range of the visible spectrum, the spectra curveprogresses at a constant rate at very low values and increases steeplyto a high value in the green to red range. The filter is particularlyadvantageous if its spectra curve has a permeability of under 0.01percent in the blue to green range and a transmission that increases toapproximately 100 percent in the red range.

The Bloom patent discloses an element for filtering infrared light. Ametal complex is employed as an infrared absorber in which the metal isa metal of the first, second or third transition metal series which willprovide a complex that is an effective infrared absorber and which iseffectively transparent to light in the visible region of the spectrum.

The Francel et al. patent discloses a method of coating a vitreoussubstrate, such as glass, with a fluid coating composition. The coatingimparts to an otherwise clear and/or transparent glass substrate thelight transmittance characteristic of amber or darker glass. Thesimulated amber glass obviates the necessity of having separate amberglass, batch-melting and auxiliary manufacturing apparatus and relatedequipment.

The Riley patent discloses an absorbent liquid coating composition thatforms a film that is applied as a protective and/or decorative coatingto glass and other normally transparent or translucent materials. Thefilm has the properties of absorbing substantially all the wavelengthsof ultraviolet, violet and blue light below approximately 490 nanometersand substantial amounts of wavelengths from 630-750 nanometers. The filmallows the transmission of selected wavelengths above 490 nanometers.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph that shows the five spectral curves of the inventionand the position of each curve within a blocking zone, a transition zoneand a transmissive zone.

FIG. 2 is a graph that shows the transmission spectra of a combinationof dyes that eliminate ultraviolet holes.

FIG. 3 is a table that lists the various conbination dyes, the time andtemperature required to provide the specific cut-on wavelengths desiredand the recommended uses for the lens.

FIG. 4 is a graph that shows the failure curve of polarizers and thepreferred area where a polarizer can be safely processed with thecombination hot-dip dyes.

FIG. 5 is a cross-section of a lens showing the dye absorbed into thesurface of the plastic and a polarizing film laminated between the twohalves of the cast or preformed plastic lens.

FIG. 6 is a cross-section of a lens showing the dye in the body of theplastic and a polarizing film laminated between the two halves of thecast or preformed plastic lens.

FIG. 7 is a cross-section of a lens having a laminated polarizing filmand a dye that is in a coating or a laminated film that is bonded to theinside or outside of the lens.

DISCLOSURE OF THE INVENTION

The ultraviolet radiation and blue light blocking polarizer lens isdesigned primarily for use with sunglasses to block horizontallypolarized light, to selectively block selected wavelengths from 300 to549 nanometers and to pass 30 to 40 percent of wavelengths longer than625 nanometers. The selective blocking is controlled by a sharp cut-onfilter selected to cut-on at either 450, 500, 515, 530, or 550nanometers. The atmosphere blocks wavelengths that are shorter than 300nanometers. Therefore, only wavelengths longer than 300 nanometers needbe blocked for safety.

Sunglasses are normally made for light or dark conditions and it iscustomary to have one or two pairs of sunglasses--one for overcast daysand another for sunny days. The inventive lenses found to be usable overa wide range of lighting conditions from dark rainy days to brilliantdesert sun. This unexpected usefulness, under such a wide range of lightconditions, is thought to be caused by a psychophysiological (orphoto-neurologic) effect resulting from the reduction of high intensitystimulation in local areas of the visual field in conjunction with theremoval of the blue light stimulation.

Another important and unexpected advantage of the inventive lens is thestrong improvement in vision provided in bright light without discomfortto the eye. In other words, the user simultaneously sees very clearlywith no discomfort from this intensely clear vision. It is hypothesizedthat this phenomenon is also a result of a photo-neurologic orpsychophysical response to the removal of blue light and high intensityglints reflected into localized areas in the visual field.

The removal of these glints and blue light appear to act synergisticallyto change the behavior of the retina resulting in the increased visualsensitivity and inducing a calming effect to the user. The inclusion ofa polarizer substantially enhances the calming effect. It is againhypothesized that the removal of the high intensity areas of the visualfield affects the neural response to the light and thus increases thecalming effect of the blue blocking alone.

A general trait of sensory systems is that the sensitivity of the systemto information input is affected by the intensity of the stimulipresented to it. In the case of the eye, damage is principally caused byintense exposure to short wavelength radiation. In the case of a visualfield where there is a diffusely illuminated area and a specularreflection of the sun in that area, the retina is most sensitive todamage from the contribution of the specular portion.

The eye is able to see over a wide range of lighting conditions bychanging the sensitivity of the retina as a function of the light inputand by changing the diameter of the pupil. The settings for thesefactors are in part based on a tradeoff between a need for safety to theretina and the need to see well. Since the specular sources aredisproportionately effective in causing damage to the retina, it isreasonable to hypothesize that specular sources would bedisproportionately effective in supplying sensitivity settings to theretina. The cellular site for this effect could be Ricco's area in theganglion cell receptive field center since it is known to be involved insetting the gain of receptor cells in the retina for simple brightness.Accordingly, the wavelength (or blueness) of a specular source, and theintensity of a specular source should enter into the control of theinformation handling of the retina and the apparent result is referredto as the "blue-glint retinal response." This effect was unknown beforethe reduction to practice of the instant invention.

Information processing in the eye enters into many neurologicalresponses in the brain. In particular, the eye supplies informationwhich sets neuroendocrine levels appropriate to sleep and alertness. Ithas also been suggested that light level and spectral composition enterinto seasonal behavior patterns involved in mood and sex hormone levels.Since the blue-glint information processing response allows the blue,high intensity light to be disproportionately effective in stimulatingsensitivity responses, it may also be involved in the calming effectwhich is far beyond that noted from blue blocking lenses alone. Theeffect of the blue glint removal may not be limited to the retina, butmay also have a psycho-physical effect on the brain. The brain may beaffected as a result of the blue-glint retinal response, therebyaffecting mood and instilling the observed calming effect.

This blue glint phenomenon may have evolved in response to theparticular damaging effects of high intensity blue light on the retina.There is a theory of retinal radiation damage involving the concept ofdaily damage accumulation and of renewal mechanisms that repair thedamage by removing and replacing the damaged molecules and structures orcells. In addition, by-products of the renewal process (amino acidsequencing defects in proteins and the formation of other nondegradablemolecular debris such as lipofuscin) can also accumulate resulting inimpaired cell function. Under this theory, the retinal cellsprogressively accumulate damage, and when damage rates are higher due toharmful chemical or radiation exposure, the accumulation of damage isalso higher.

Superimposed upon this general increase in debris from the renewalprocess in the retina, there are shorter term accumulations of damagewhich occur during light exposure during the day which is then removedand replaced overnight. However, the renewal mechanisms have finiterates of repair, and if the light exposure is over a certain point, therenewal processes overnight are insufficient to bring the retina back toclose to its previous state by morning. This damage is similar to theprogressive accumulation of damage described above, and contributes toit, but it is in addition to this progressive accumulation of damage,and affects the function of the eye on a shorter time scale. An exampleof this is the repair activity noted in night vision degradation inexperiments with lifeguards. For damage above the night visiondegradation threshold, the experiment disclosed that the night visionwould gradually improve overnight but that the gains would lag below thelevel of vision the night before. If adequate protection was givenduring the day however, the eye's night vision would return to normalafter a few weeks as the cell renewal processes caught up.

With longer exposure times, the time available for renewal mechanisms toact become more significant. For solar retinitis, the time scale isshort. The rate of damage is sufficiently high to cause a lesion and thecontinuing exposure would result in blindness in a short time. Nightvision degradation, in contrast, requires less irradiation and thuslower damage rates than solar retinitis and is more affected on a day today basis by the efficacy of repair mechanisms of the eye.

When the rate of damage overall is equal to the rate of renewal overall,a threshold is reached above which damage gradually accumulatesresulting in the progressive loss of vision. This damage threshold isused in setting the standards discussed in this disclosure and is thebasis for the design of the inventive lens.

Functional impairment of the retina is associated with a threshold fordamage for a particular time scale of exposure. The threshold for aretinal lesion is at a higher irradiance or for a longer time scale thanfor night vision impairment.

This lower irradiance, longer term damage which has been quantitativelydemonstrated by researchers, has shown that for a given wavelength,smaller irradiances result in damage if the exposure time is longer andfor a given irradiance, longer wavelengths can produce damage if theexposure time is longer. To extrapolate to longer time scales and lowerirradiances, the efficiency of renewal mechanisms would become moresignificant in determining the threshold for functional impairmentresulting from exposure to damaging influences such as radiation. It hasnot been proven that the damage mechanism is the same for short timescales as long ones, and the site of injury has been suggested to shiftfrom the retinal pigment epithelium to the receptor layer for long termdamage. However, the basic idea of radiation induced damage due to theformation of impaired renewal mechanisms still holds even in this caseas well as an action spectrum similar if not identical to the blue lighthazard spectrum. This suggests that for long time scales such as alifetime, the renewal mechanisms are important determinants of the longterm prognosis of blindness or eye health.

Damage from high energy visible (blue and violet) and UV photons is dueto the formation of reactive molecules which form when cellularmaterials are struck by the photons. The repair mechanisms involvetransport and conversion of highly reactive molecules to less reactiveforms without allowing these molecules to react with the cellularmaterials. The lysosomal enzyme systems that remove damaged moleculesare capable of handling sub-threshold damage rates. However, over thethreshold, damaged molecules accumulate resulting in impairment to thefunctions of the cell as the reactive molecules react with the cellularmaterials and enzymes. This "threshold dependent" damage would be aboveand beyond the "normal" accumulation of lipofuscin associated withrenewal processes. Therefore it is advisable to stay below the thresholdin the interest of limiting long term damage to the retina.

The irradiance relative to the threshold is then the single mostimportant factor determining the safety and related comfort of asunglass lens. The mathematical analysis below has shown that under somelight conditions, a filter without a polarizer is insufficient to staybelow the calculated threshold. Accordingly, in the area of a glintimage on the retina, the tissues on a local scale are closest tothreshold and likely to go over it. In order for a conventional sunglassto be able to reduce the glints to a level where they are belowthreshold, the lenses would have to be so dark as to be nearly uselessfor vision. The damage to the retina takes place on a small spatialscale, and thus the threshold crossing effect of the glints is undersome conditions the only significant damage to the eye duringirradiation with blue blocking lenses.

The intensity of photons in the glint can also contribute to thephotochemical damage due to the heating of the retina in the vicinity ofthe glint. High intensity glints of light in the visual field cause alocalized area of the retina to be exposed to far more photons persecond than outside the focussed glint area. Even wavelengths which arerelatively harmless (longer than 600 nanometers) can, under somecircumstances cause damage due to thermal heating of the retina in thoseareas. Thermal heating potentiates photochemical degradation of thereceptor segments in the retinal cells, thus encouraging damage to therods and cones of the eyes. By removing the heated areas, the blue lightwhich impinges on the retina is thus rendered less harmful. Theadditional contributory effect of the glint may cause the damagethreshold to be passed in a given retinal cell, and photochemical damagewould then occur in that location of the glint image. Without the glint,the blue photons may be below threshold damage level and no irreversibledamage would occur. Removal of the glints removes the heating and thusthe passing of the threshold for damage by the blue light in thoseareas. This thermochemical potentiation of damage has not been takeninto account quantitatively in this analysis.

Removing the glints substantially improves the safety of the sunglasswithout resorting to the more extreme blue blocking that would benecessary to achieve the same degree of retinal safety. It has beenfound by researchers and those companies which make blue blockingglasses, that many people are disoriented and even nauseated by blueblocking lenses. The effect was so strong that many companies sought themedical market only, ignoring the majority of sunglass wearers in theU.S.

Blue light exposure has also been shown to affect the levels of thyroxindifferently from other wavelengths of light in an animal study and thiseffect might occur in humans. Furthermore, in other animal studies, theblue light has been shown to block the release of melatonin from thepineal gland better than other wavelengths of light. Thus, wearing blueblocking glasses may result in an increased release of melatonin fromthe pineal. The ramifications of this melatonin increase may be farreaching since melatonin has been shown to affect other hormonal systemswhich in turn affect metabolism and sex hormones. It is known thatmanic-depressives' melatonin levels are hyper-sensitive to light levels.Additionally, some people have "winter depression" during the dark shortdays of winter which was then relieved by exposure to high intensityblue-rich fluorescent lights. Melatonin is also known to increaseretinal degeneration under high light illumination.

Researchers generally agree that humans are genetically adapted to aforest cover environment and thus would normally get less blue lightexposure and thus more melatonin. Hence wearing the inventive lenses mayreturn melatonin levels to a higher and more historically normal andmore healthful level. While blue blocking to some degree may modify theendocrine systems in animals, it appears likely that they modify themfor the better, returning the system to a more healthful, natural andbalanced state.

For these reasons, the blue blocking is desirable but should notnecessarily be done to excess so long as the retina is well protected.Since the benefits to the retina of blocking blue light are very firmlyestablished, some blue blocking is desirable. The ideal situation existswhere the glints are removed, so that the illumination is relativelyuniform. Under these conditions, a minimum of blue light can be blockedwhile still keeping all retinal cells below threshold.

Accordingly, a range of lenses which selectively block from 300 to 450nanometers and which have a sharp cut-on filter from 450 to 550nanometers with a polarizer have been selected so that the individualhas an appropriate amount of short wavelength blocking for adequateprotection under a wide range of light environment conditions.

Analysis Demonstrating the Value of the Inventive Lens

An analysis was performed to calculate in absolute terms the intensityof hazardous light reaching the eye under various circumstances withoptical filters interposed between the eye and the light source. Thisanalysis considers the effect of polarizers on reducing the intensity oflight under different hazardous outdoor light conditions. The hazardswere compared with known exposure levels for solar retinitis and nightblindness resulting in absolute standards for sunglass performance.Under some circumstances only the inventive lens were sufficient to meetthe standard.

It has been shown that high levels of blue light (400-500 nanometersrange) reaching the retina are harmful to visual performance and thehealth of the eye. In order to determine the hazard under real andpertinent conditions, models of actual light environment conditions weremade. Within those environments, two broad categories of hazardous bluelight sources were considered: "glints" and "extended sources".

"Glints" consist of essentially specular reflections of the sun. Thesesources have some degree of polarization due to the nature ofreflections. Glints also subtend a small angle of the eye's field ofview. The "extended sources" included diffuse reflections of the sunfrom such high reflectivity surfaces as snow and clouds as well as theblue light of the sky. These sources subtend a large angle in the eye'sfield of view and expose large areas of the retina to an essentiallyuniform level of illumination.

Calculation of Hazard Values for Specular Reflection Sources

A glint is a reflected image of the sun as viewed by the observer's eye.The plane of incidence (defined by the incident and reflected ray) isvertical for all reflections studied in this analysis. This is becausemost commonly encountered reflections of the sun are reflected fromhorizontal or nearly horizontal surfaces. The size of this image isgiven by:

    y.sub.i =(y.sub.sol /s.sub.sol)*(r/2)                      [1]

Where:

y_(i) =diameter of the image of the sun.

y_(sol) =diameter of the sun.

s_(sol) =distance to the sun.

r=radius of curvature of the reflective surface (r>0→convex reflector)

The distance the image of the sun lies behind the convex reflector isgiven by:

    s.sub.i =-1/(2/r+1/s.sub.sol)                              [2]

Where:

s_(i) =The distance the image of the sun lies behind the convexreflector.

s_(sol) =distance to the sun.

r=radius of curvature of the reflective surface (r>0→convex reflector)

The total radiance of the image of the sun is given by:

    L.sub.i =R*L.sub.sol *T.sub.atmosphere.                    [ 3]

Where:

L_(i) =The radiance of the image of the sun.

R=the combined reflectance of the reflecting surface.

T_(atmosphere) =the transmission of the Earth's atmosphere.

L_(sol) =radiance of the sun as viewed from above the Earth'satmosphere.

The preceding analysis does not consider polarization effects. Toconsider polarization effects, different reflectance coefficients mustbe used for the two axes of polarization defined by the plane ofincidence. The light emanating from the image of the sun is composed ofboth horizontally polarized light and vertically polarized light. Sincewe are assuming a vertical plane of incidence, and since sunlight israndomly polarized, the radiance of vertically polarized light andhorizontally polarized light are given by:

    L.sub.ihorizontal =L.sub.iperp =(L.sub.sol /2)*T.sub.atmosphere *R.sub.perp [ 4a]

    L.sub.ivertical =L.sub.ipara =(L.sub.sol /2)*T.sub.atmosphere *R.sub.para and,                                                      [4b]

    L.sub.ihorizontal +L.sub.ivertical =L.sub.i                [ 4c]

    (R.sub.perp +R.sub.para)/2=R                               [4d]

Where:

L_(ivertical) =the radiance of vertically polarized light radiating fromthe image of the sun in Watts/(cm² *steradian)

L_(ihorizontal) =the radiance of horizontally polarized light radiatingfrom the image of the sun in Watts/(cm² *steradian)

R_(perp) =the reflectance coefficient for light which is polarizedperpendicular to the plane of incidence (horizontally polarized light)

R_(para) =the reflectance coefficient for light which is polarizedparallel to the plane of incidence (vertically polarized light)

The factor of 2 enters in because half of the incident sunlight ishorizontally polarized and half is vertically polarized.

The reflectance coefficients for reflection of light off of a dielectricmaterial (such as glass or water) are given by:

    R.sub.perp =[sin (q.sub.i -q.sub.t)/sin (q.sub.i +q.sub.t)].sup.2 [ 5a]

    R.sub.para =[tan (q.sub.i -q.sub.t)/tan (q.sub.i +q.sub.t)].sup.2 [ 5b]

    q.sub.t =(n.sub.i /n.sub.t)*q.sub.i                        [ 5c]

Where:

q_(i) =the angle of incidence measured relative to the normal of theplane.

q_(t) =the angle of transmittance of the light into the dielectricmedium.

n_(i) =index of refraction of incident medium (air)

n_(t) =index of refraction of transmitted medium (glass, water, etc)

Rpara=Reflectance coefficient for light polarized parallel to the planeof incidence (vertically polarized light). Rpara=(Intensity of reflectedlight which is polarized parallel to plane to incidence)/(Intensity ofincident light which is polarized parallel to plane of incidence)

Rperp=Reflectance coefficient for light polarized perpendicular to theplane of incidence (horizontally polarized light). Rperp=(Intensity ofreflected light which is polarized perpendicular to plane ofincidence)/(Intensity of incident light which is polarized perpendicularto plane of incidence)

The angle subtended by the image of the sun as viewed by the observer'seye is given by:

    a.sub.e =Atan(y.sub.i /(s.sub.e +s.sub.i))                 [6])

Where:

a_(e) =The angle subtended by the image of the sun as viewed by theobserver's eye.

y₁ =diameter of the image of the sun.

s_(e) =distance between observer's eye and reflecting surface.

s_(i) =distance image is behind reflecting surface.

The corneal irradiance caused by the image of the sun is given by:

    E=pi*L.sub.i *(sin (q.sub.e)).sup.2                        [ 7]

Where:

E=corneal irradiance caused by image of the sun

L_(i) =radiance of the image of the sun

q_(e) =a_(e) /2=half angle subtended by the image of the sun as viewedby the observer's eye.

The different reflection coefficients for the two axes of polarizedlight lead to separate radiances and irradiances for each axes ofpolarization. The irradiances for the horizontal and verticallypolarized light are given by:

    E.sub.horizontal =pi *L.sub.ihorizontal * (sin (q.sub.e)).sup.2 [ 8a]

    E.sub.vertial =pi *L.sub.ivertical *(sin (q.sub.e)).sup.2  [ 8b]

Where:

E_(horizontal) =the corneal irradiance of horizontally polarized lightcaused by the image of the sun.

E_(vertical) =the corneal irradiance of vertically polarized lightcaused by the image of the sun.

The different reflection coefficients for the two axes of polarizedlight lead to separate radiances and irradiances for each axis ofpolarization. The reflectance coefficients shown above indicate that thelight which is polarized perpendicular to the plane of incidence isreflected more strongly. Consequently, polarized sunglass lenses areoriented so that they block the light which is polarized perpendicularto the plane of incidence. Since the polarizers used are aligned so thatthey block virtually all of the light which is polarized perpendicularto the plane of incidence, the total corneal irradiance after the lightfrom the image of the glint has passed through the polarizer is givenby:

    E.sub.p =E.sub.vertial =pi*L.sub.ivertical *(sin (q.sub.e)).sup.2 =pi*(L.sub.sol /2)*T.sub.atmosphere *R.sub.para *(sin (q.sub.e)).sup.2 [ 9]

The standards concerning exposure to hazardous levels of blue light areexpressed in terms of hazard-weighted irradiance or hazard-weightedradiance. This hazard function incorporates the fact that certainwavelengths of light are more damaging to the retina than others. Ingeneral, the shorter the wavelength of light the more damaging it is.This is due to the photochemical nature of the actinic damage mechanism.However, the ultraviolet (UV) wavelengths of light are largely absorbedby the cornea, lens, and aqueous and vitreous humors of the eye andtherefore very little of the short wavelength UV light reaches theretina. These two effects combine to produce a retina hazard functionwhich peaks in the blue region of the spectrum at about 450 nm. Theequations for calculating the hazard weighted radiances and irradiancesare given by:

For extended sources: ##EQU1## Where: L_(b) =the hazard weightedradiance in W/(cm^(2*) sr)

L_(source) (I)=the spectral radiance of the source as a function ofwavelength in W/(cm^(2*) sr*nm)

BLH(I)=the blue light hazard function as a function of wavelength

Δl=the interval of wavelength at which measurements are taken and thecalculation is made. In this study spectral data was taken at intervalsof 5 nm.

And for point sources subtending less than 11 millirad (approximately0.62 deg.) we have: ##EQU2## Where: E_(b) =the hazard weightedirradiance in W/cm²

E_(source) (I)=the spectral irradiance of the source as a function ofwavelength in W/(cm^(2*) nm)

BLH(I)=the blue light hazard function as a function of wavelength

Δl=the interval of wavelength at which measurements are taken and thecalculation is made. In this study spectral data was taken at intervalsof 5 nm.

The standards given for the two types of hazardous sources are given byresearchers in the field as follows:

    L.sub.b <=0.01 W/(cm.sup.2* sr) for t>=10.sup.4 seconds    [12]

    E.sub.b <=1 microwatt/cm.sup.2 for t>=10.sup.4 seconds     [13]

To calculate the effect of a spectrally selective filter on the hazardweighted irradiance and radiance of a hazardous source, the spectrum ofthe source as viewed through the selective filter must be calculated asfollows:

    L.sub.filteredsource (I)=T.sub.filter *L.sub.source (I) and, [14]

    E.sub.filteredsource (I)=T.sub.filter *E.sub.source (I)    [15]

The blue light hazard of the source when viewed through the filter cannow be calculated by inserting L_(filtered) source (I) in place ofL_(source) (I) in eqn [10] and inserting E_(filteredsource) (I) in placeof E_(source) (I) in eqn [11].

Finally the blue light hazard of a glint as viewed through thecombination of a spectrally selective filter and a properly orientedpolarizer is calculated by substituting L_(ivertical) in place ofL_(source) in eqn [14] and substituting E_(ivertical) in place ofE_(source) in eqn [15] and proceeding with the calculation by insertingthe resulting source radiance and irradiance in eqns [10] and [11]respectively.

In this analysis these extended sources are assumed to have a negligibledegree of polarization. Blue skylight is horizontally polarized to somedegree in the direction opposite the position of the sun but mostextended sources do not polarize light appreciably.

The quantity of importance for extended source optical hazards is theradiance, L_(d). For extended sources such as the blue sky, the radianceis measured directly and weighted by the procedure described by eqn [11]to produce the blue light hazard weighted radiance. For extended sourcesilluminted by the sun which are essentially white lambertian scattererssuch as fresh snow, dry white sand, or the top of a cloud deck theradiance is given by:

    L.sub.d =R.sub.d *L.sub.sol *(sin (q.sub.sol )).sup.2      [ 16]

The blue light hazard weighted radiance of solar illuminated extendedsources is given by:

    L.sub.db =R.sub.d *L.sub.solb *(sin (q.sub.sol)).sup.2     [ 17]

Where:

L_(db) =the blue light hazard weighted radiance of the extendedscattering source which is illuminated by the sun.

R_(d) =the diffuse reflectance coefficient of the scattering surface.

q_(sol) =the half angle subtended by the sun.

L_(solb) =the blue light hazard weighted radiance of the sun ascalculated below: ##EQU3## Where: L_(solb) =the hazard weighted radianceof the sun in W/(cm² *sr)

L_(sol) (I)=the spectral radiance of the sun as a function of wavelengthin W/(cm² *sr*nm)

BLH(I)=the light blue hazard function as a function of wavelength

Δl=the interval of wavelength at which measurements are taken and thecalculation is made. In this study spectral data was taken at intervalsof 5 nm.

DERIVATION OF METHOD FOR QUANTITATIVELY SELECTING CUT-ON WAVELENGTHS:

Equations [11] and [13] can be combined to give: ##EQU4## Where: E_(b)=the hazard weighted irradiance in W/cm²

E_(source) (I)=the spectral irradiance of the source as a function ofwavelength in W/(cm² *nm)

BLH(I)=the blue light hazard function as a function of wavelength

Δl=the interval of wavelength at which measurements are taken and thecalculation is made.

The corneal irradiance which results after the incident light has passedthrough the spectral filter=E_(bfiltered). By substitutingE_(filteredsource) (I) for E_(source) (I) and E_(bfiltered) for E_(b) inequation [18] we have the following equation for E_(bfiltered) :##EQU5## Where: E_(filteredsource) (I)=the spectral irradiance of thesource after it has passed through the spectrally selective filter.

E_(bfiltered) =the hazard weighted irradiance of the source after it haspassed through the spectrally selective filter.

Substituting equation [15] into [19] yields: ##EQU6## Where: T_(filter)(I)=the spectral transmission of the sunglass filter withoutpolarization.

Since the polarizers used are aligned so that they block virtually allof the light which is polarized perpendicular to the plane of incidence,the total corneal irradiance after the light from the image of the glinthas passed through the polarizer is given by:

    E.sub.p =E.sub.vertical                                    [ 9]

Therefore, only E_(vertical) (I), the vertical component of E_(source)(I), reaches the cornea. Thus the total corneal irradiance, inWatts/cm², which results after the incident light has passed through thespectrally selective filter and the polarizer is defined asE_(bpolfiltered) and is given by: ##EQU7## Where: E_(vertical) (I)=theunfiltered corneal spectral irradiance of vertically polarized lightcaused by an image of the sun in W/(cm² *nm).

To choose the cut-on wavelength which is appropriate for theenvironmental conditions, typical values of E_(vertical) (I), thevertically polarized component of the unfiltered corneal irradiance,must be measured. Equation [22] may now be solved iteratively for thecut-on wavelength, l_(cut-on) wavelength, which results in a spectrumwhich reduces the corneal irradiance to a safe value (←1 microwatt/cm²for solar retinitis, ←0.02 microwatt/cm² for night vision loss).##EQU8## Where: E_(bpolfiltered) =the total corneal irradiance, inWatts/cm², which results after the incident light has passed through thespectrally selective filter and the polarizer.

E_(vertical) (I)=the unfiltered corneal spectral irradiance ofvertically polarized light caused by an image of the sun in W/cm² *nm).

T_(filter) (I)=the spectral transmission of the sunglass filter withoutpolarization.

BLH(I)=the blue light hazard function as a function of wavelength

Δl=the interval of wavelength at which measurements are taken and thecalculation is made.

l_(cut-on) wavelength =the cut-on wavelength best suited to the usageenvironment described by E_(vertical) (I).

A similar argument can be made for extended sources. This derivationuses equations [10], [12], and [14] instead of equations [11], [13], and[15]. This argument yields the following equation which can be solvediteratively for the cut-on wavelength, I_(cut-on) wavelength, whichreduces the radiance viewed by the eye of the sunglass wearer to a safelevel (10 mWatt/(cm² *sr) for solar retinitis, 0.2 mWatt/(cm² *sr) fornight vision loss): ##EQU9## Where: L_(bpolfiltered) =the total cornealradiance, in Watt/(cm² *sr), which results after the incident light haspassed through the spectrally selective filter and the polarizer.

L_(vertical) (I)=the unfiltered corneal spectral radiance of verticallypolarized light caused by an image of the sun in Watt/(cm² *sr*nm).

T_(filter) (I)=the spectral transmission of the sunglass filter withoutpolarization.

BLH(I)=the blue light hazard function as a function of wavelength

Δl=the interval of wavelength at which measurements are taken and thecalculation is made.

I_(cut-on) wavelength =the cut-on wavelength best suited to the usageenvironment described by L_(vertical) (I).

Standards Based On Effects

There have been several research reports presented which describe themicroanatomical and functional effects of exposure to certainwavelengths of light. One of these reports found that the 35 to 50percent tansmission of conventional sunglasses was usable to provideprotection lasting longer than a day or so while 10 to 12 percenttransmission sunglasses are adequate to protect night vision for longerperiods. It has also been argued that short wavelength visible light isthe effective part of the spectrum in their observed degradation ofnight vision. From this premise, and by using the original calculationsshown above, we are able to calculate the hazard weighted radiance thesubjects were exposed to and thus determine the threshold for nightvision protection. It appears that the threshold for night visiondegradation is at approximately 0.2 mWatt/(cm² *sr). The threshold forsolar retinitis is 10mWatt/(cm² *sr).

Some retinal irradiance studies have been in terms of exposure toextended sources while others are in terms of specular sources. Theimage of a specular source is not perfectly focussed and is moved acrossthe retina by the motion of the eye resulting in a larger effective areaand lower effective irradiance than would be expected if the irradiancewere perfectly focussed in one place. A 1 microWatt/cm² point sourceproduces the same retinal irradiance as a 10 milliwatt/cm² *sr extendedsource over the area it affects. The resulting damage thresholds areshown in the Table below:

    ______________________________________                                        Thresholds for Damage                                                         Damage        Specular      Extended                                          ______________________________________                                        Solar Retinitis                                                                             1.0 microW/cm.sup.2                                                                         10.0 mW/(cm.sup.2 *sr)                            Night Vision Loss                                                                           0.02 microW/cm.sup.2                                                                        0.2 mW/(cm.sup.2 *sr)                             ______________________________________                                    

For our purposes in developing a quantitative method of choosing theappropriate cut-on wavelength, the more protective standard of 0.02microW/cm² (for point sources) and 0.2mW/(cm² *sr) for extended sources)was chosen. However, for applications where preservation of night visionis not important, the less protective standard of 1.0 microW/cm² (forpoint sources) and 10.0 mW(cm² *sr) (for extended sources) can be used.

Standards based on the above Table are presently not used in thesunglass industry and are an innovation of the inventors. The standardis referred to as the Eye Protection Factor (EPF). The EPF standard isbased on how well the sunglass blocks harmful radiation relative to thethresholds described above for a standard condition and results in arating number which a consumer can use in a manner similar to the SunProtection Factor (SPF) numbers shown on suntan lotions.

In view of the above disclosure it is the primary object of theinvention to disclose a sunglass lens design and process for making thelens that uses a combination dye and a polarizer to produce a lens thatsubstantially blocks ultraviolet radiation, blue light, and horizontallypolarized light. The result of this is a lens that:

can be used for an extended period of time without damage ordisciomfort,

improves visual acuity,

protects against long term eye damage,

preserves night vision,

reduces risk of eye disease,

reduces the onslaught of radiation which results in aging of the eyetissues and taxes regenerative processes in the eye.

In addition to the primary objects it is also an object of the inventionto have a lens that is:

cost effective and safe to own,

cost effective and safe to manufacture,

mechanically easy to handle and use,

adaptable to a variety of sunglass frames,

adaptable to a variety of visual environments,

can be used in applications other than for sunglasses

These and other objects and advantages of the invention will becomeapparent from the subsequent detailed description of the invention andthe claims taken in conjunction with the accompanying drawings.

BEST MODE FOR CARRYING OUT THE INVENTION

The best mode for carrying out the inventive Ultraviolet radiation andblue light blocking polarized lens 10 is presented in terms of apreferred embodiment that is primarily designed for mounting on a pairof sunglasses. The lens 10 substantially blocks horizontally polarizedlight and selectively blocks wavelengths in the electromagnetic spectrumthat lie between 300 and 549 nanometers and allows 30 to 40 percent ofwavelengths in the visible portion of the spectrum, that are longer than625 nanometers, to be transmitted. The selective blocking is controlledby a sharp cut-on filter selected to cut-on at either 450, 500, 515,530, or 550 nanometers. Only wavelengths longer than 300 nanometers needbe blocked due to atmospheric absorption of shorter wavelengths.

The lens 10 in the disclosure that follow refers to various terms. Tofacilitate the understanding of the invention, these terms are initiallydefined.

Electromagnetic spectrum. For the purpose of this invention, thespectrum has a lower limit of 300 nanometers and an upper limit of 780nanometers. The visible portion of the spectrum is further defined asfalling between 400 and 780 nanometers.

Transmission. The percentage of light that is passed through a lens.

Blocking. The opposite of transmission and is a measure of thepercentage of light that is either reflected by the surface or surfacecoatings or absorbed by the dye or plastic of the lens.

Substantially blocking. When used with reference to wavelengths, it isdefined as blocking over 99 percent of the incident radiation at eachand every wavelength. When used with reference to polarization, it isdefined as blocking 80 percent or more of the horizontally polarizedincident radiation at each and every wavelength. Conversely,substantially transmitting, when used with reference to wavelengths, isdefined as transmitting more than 1 percent of the incident radiation ateach and every wavelength. When substantially transmitting is used withreference to polarization it is defined as transmitting 20 percent ormore of the horizontally polarized incident radiation at each and everywavelength.

Sharp cut-on. For the purpose of this invention, sharp cut-on is definedin the context of a dye or filter, having a cut-on slope that rises morethan one half percent (0.5%) change in transmission for every onenanometer of increasing wavelength change. The cut-on slope is thatportion of the transmission spectra of a cut-on dye that represents thetransition between substantially blocking region and the substantiallytransmissive region. A cut-on filter is an optical filter thatsubstantially blocks all wavelengths shorter than the cut-on wavelengthand substantially transmits all wavelengths that are longer than thecut-on wavelength. The cut-on wavelength is that wavelength in thetransition zone at which the tranmission is 1 percent.

Combination dye. For the purpose of this invention, a combination dye isdefined as being made from a mixture of two dyes who's ultraviolettransmission holes do not substantially overlap.

The preferred embodiment of the invention, as shown in FIGS. 1 through8, is comprised of the following seven major elements: a plastic lens12, a sharp cut-on filter 14, a horizontally polarizing film 16, acombination dye 18, a dispersed orange three sharp-cut-on dye 20, adispersed red two sharp-cut-on dye, and a disperesed yellow twenty-threesharp-cut-on dye 24.

The lens 10 as used in this invention is primarily a blocking lensrather than a transmissive lens and is cast from an optical plastic oroptical glass. In the preferred embodiment, the lens is cast from anoptical hard-resin plastic made from a di-allyl glycol carbonate monomersuch as a CR-39 polymer. CR-39 is a registered trademark of thePittsburgh Plate Glass Company having its principal offices in theUnited States of America. The CR-39 polymer possesses properties thatunder controlled conditions allows the lens to be easily dyed with theselected dispersed dyes, described infra, that provide the requiredwavelength blocking.

Sunlight is composed primarily of visible light and invisible radiationsknown as Ultraviolet and Infrared. Most persons exposed to bright light,especially sunlight, for any period of time are more comfortable whenwearing sunglasses that block wavelengths in the 400 to 780 nanometerrange. Conventional sunglass lenses that block in this range reduceexcessive glare, which can cause eye discomfort but they hamper visualacuity because of their necessarily low transmission.

The blocking feature of the inventive lens 10 is achieved by the sharpcut-on filter 14 which is used in combination with the horizontallypolarizing film 16. The function of the filter 14 is best understood byreferring to FIG. 1 which discloses the spectral curves of theinvention.

The spectral curves are divided into a blocking zone, a transition zoneand a transmissive zone. The curves define the transmission spectra of afamily of sunglass lenses having sharp cut-on filters at wavelengths of450, 500, 515, 530, and 550 nanometers.

If a filter 14 having a cut-on at 450 nanometers is selected, theblocking zone and the transmissive zone are common to other members ofthe family. In this case, wavelengths between 300 and 449 nanometer aresubstantially blocked up to the transiton zone where the sharp cut-onfilter 14 cuts-on at 450 nanometers and steeply rises up to thetransmissive zone where 30 to 40 percent of the wavelengths that arelonger than 625 nanometers are transmitted.

If a cut-on filter 14 other tha at 450 nanometers is selected, the rangeof the blocking zone increases (displaced horizontally). For example, ifa 500 nanometers cut-on filter is selected, wavelengths between 300 and499 nanometers would be blocked up to and into the transition zone wherethe sharp cut-on filter 14 would cut-on at 500 nanometers; likewise, acut-on at the maximum 550 nanometer would allow wavelengths between 300and 549 nanometers to be blocked before the cut-on filter cuts-on at 550nanometers. In all cases of the preferred embodiment, the transmissivezone, beyond 625 nanometers, remains fully open transmitting between 30to 40 percent at each and every wavelength out into the infrared region.In the preferred embodiment, 30 to 40 percent of wavelengths longer than625 nanometers, are transmitted. However, the transmittance of thetransmissive zone beyond the 625 nanometer point can be increased to anyrange between 10 and 90 percent by the proper selection of thecombination dye 18 and the polarizing film 16.

The principal novelty of the invention is in the ability of the lens 10by means of the sharp cut-on filter 14 in combination with the polarizer16 to block ultraviolet radiation, blue light and horizontally polarizedlight. While a calming effect is achieved by wearing only blue blockinglenses, the inclusion of the polarizer 16 substantially increases thecalming effect and substantially improves vision without visiondiscomfort. Additionally, the inventive lens allows a specific degree ofsafety without affecting the hormonal balance of the body any more thannecessary. These surprising and unexpected results have been explainedby way of a hypothesis after the combination was reduced to practice andthe effects were experienced first hand. The complete explanation ofsome effects must await further understanding of the human brain and theinteraction of the human eye with light. In contrast, the limitedimprovement in visual acuity and eye protection afforded by theelimination of the Ultraviolet radiation and the reduction of blue lightcontent is well recognized by researchers in the field.

The process that resulted in a successful reduction to practice of theinnovative lens 10 was not obvious at the outset. The economicproduction of UV and blue blocking polarizing sunglasses is hampered bythe fact that the currently manufactured plastic lens polarizersgenerally consist of a sheet of heat sensitive polarizing film laminatedbetween two layers of the CR-39 polymer lens. The polarizer is formed bystretching the thin film so that the film molecules are aligned in a waythat light passing through the lens is polarized. When this film islaminated in the cast CR-39 polymer it can withstand the heating that isnormally used to hot-dip dye lenses with cosmetic tints. These tints areusually very light shades of pastel colors that add a decorative andindividualizing feature to the lens. The requirement for dying the lensto the level that is required by the instant invention for full eyeprotection and maximum visual acuity required a time and temperature inthe hot-dip dye vessels that destroyed the polarizing effect of the lens10.

It is also known in the art that commercially available dispersed sharpcut-on dyes suitable for the hot-dip dying of CR-39 plastic lenses havea significant UV radiation transmission. This UV transmission issometimes referred to as a "UV hole". The cut-on dyes, as shown in FIG.2, Curves A and B, used in this invention each have a "UV hole". If thelens 12 is allowed to become sufficiently dark by extending the dyetime, the UV hole will be absorbed to less than one percent.Unfortunately, the time required for this UV reduction will cause thepolarizer to fail due to the time the polarizing film 16 is heated inthe dye and exposed to the dye chemicals.

The minimum time the lens 12 must be in the dye is determined by howlong it takes to fill the UV hole. By using the combination dye 18, asshown in FIG. 2 Curve C, the time and temperature required to remove theUV holes can be reduced as shown in FIG. 2 curve A to allow thepolarizer film 16 to survive the manufacturing process.

The hot-dip dyeing process is the most commonly used process for dyingophthalmic lenses and is the basis for the best mode process. The dyesthat are used are dispersed dyes, that is, they are molecules of oilsoluble dye encased in a surfactant skin. The dyes are dispersed inwater at a temperature of 98±1 degree centrigrade. When an encasedmolecule of dye contacts the plastic surface the surfactant skin breaksand the oil soluble dye molecule diffuses into the surface of theplastic lens. Increasing the dye concentration in the boiling waterdispersion does not increase the dyeing rate significantly but thedanger that the dispersion will break down increases dramatically. Whenmany dye molecules collide with one another their surfactant skin canbreak down and they can aggregate into a greasy lump of dye moleculesthat have lost their surfactant skins. This lump sticks to the lenssurface where it will form a visible spot on the lens. If the particularsharp cut-on dispersed dye is allowed to diffuse into the plastic for along enough time and at a high enough temperature the UV hole will bereduced to acceptable levels to provide adequate eye protection and therequired cut-on wavelength.

What was not known to the ophthalmic lens dying industry was the factthat some dyes have their UV holes at slightly different wavelengthsfrom one another. This off-set of the UV holes in different dyes is thediscovery that induced the process part of the instant invention.

The instant invention makes the sharp cut-on dyeing of heat sensitivepolarizers technically and economically feasible. In the Best ModeTable, as shown in FIG. 3, it can be observed that a combination of adispersed yellow twenty-three dye 24 and a dispersed orange three dye 20will produce the desired results of a sharp cut-on filter in the shorter(light orange) wavelengths; and a combination of a dispersed orangethree dye 20 with a dispersed red two dye will produce a sharp cut-onfilter with longer (dark orange) wavelengths. The dye concentrationswere empirically determined to produce a combination of dyes that wouldnot produce the greasy lumps and would dye the heat sensitive polarizerlens fast enough that they would not be destroyed. The best mode tableof FIG. 3 provides the dye combination 18, the required time andtemperature to provide the specific cut-on wavelength desired. The tablealso includes the recommended uses for the UV and blue blockingpolarizing lens 10. Although not considered a preferred method, the lensmay be applied by the combination dye at a temperature of 37±1 degreecentigrade where the time is between 7 and 10 days.

The polarizer 16 combined with the lens 12 adds a polarizing screen thatblocks horizontally polarized light. The film used, as previouslymentioned, is sensitive to chemical and temperature damage. Thus apolarized film that is exposed to heat and chemicals (such as a dye)after a period of time will fail and cease to block the polarized light.A typical polarizing film 16 failure curve is shown in FIG. 4 Curve A.The area above Curve A constitutes the polarizer failure region whilebelow Curve A is the safe region. Therefore, to safely dye polarizinglenses, the dyes must be selected so that the required optical densitycan be achieved within the enclosed area shown in FIG. 4 area B which isbelow the polarizer failure Curve A. In other words, the dye time andtemperatures shown in FIG. 3 must be selected to fall within the saferegion shown in area B. The downward inflection of Curve A is due to thechemical degradation of the polarizing lens that occurs after extendedperiods of time in the dye at low temperature.

A search was made for sources of polarizers which had as high a Curve Aas possible. One such lens, a heat resistant polarizer which did notdelaminate or fail at required time and temperature, is known as"R-plano smoke color as in invoice 10-324" and is procured from theAlpha Company Ltd. in Japan. Of the numerous sources examined, anexceptionally heat resistant lens manufactured by the Polarlite Co. inSeattle, Wa., was also found that could sometimes by dyed with a singledye (orange or yellow) for longer times and higher temperatures.However, because of the expensive heat resistant lens, the use of onedye is not considered the best mode, but it is another possible way tomake the lens 10.

Other ways to make the polarized lens include:

laminating a film onto or between a pre-dyed UV and blue blocking lensblank,

dying the lens with an embedded polarizer in a solvent dye, and/ormixing the dye into the monomer before molding around a polarizing film.

While under some circumstances these techniques could be desirable,their complexity, tooling costs and minimum manufacturing quantitiesmake them economically unfeasible for smaller scale operations.

For intermediate scale production, lenses can be dyed using the bestmode time, temperatures and dye concentrations shown in FIG. 3.

For large scale production, lenses can be dyed using the best mode time,temperatures and dye concentrations in FIG. 3.

After the lenses are dyed they are edged by standard industrial edgingmachines well known in the ophthalmic industry. The lenses are thenmounted in metal or plastic frames suitable for the various occupationsand recreations mentioned in the Best Mode Table of FIG. 3. Before thecompleted sunglasses are shipped they are compared to spectral standardsto insure they meet the required cut-on filter requirements and therequired polarization performance. The sunglasses are inspected forimperfections and proper assembly in the frames.

The polarizing film 16 as used with various combinations of dyelocations is shown in crossection in FIGS. 5, 6, and 7.

In FIG. 5, the dye is absorbed into the surface of the plastic lens 12and the polarizing film 16 is laminated between two lens halves of castor preformed plastic. The dye in this case is absorbed into the lenssurface by a hot-dip dispersed dye process or a cold-dip solvent dyeprocess.

In FIG. 6, the dye is mixed into the cast or preformed plastic lens 12before the plastic is cast. Two halves are then laminated on either sideof the polarizing film.

In FIG. 7, the polarizing film 16 is laminated and the dye is in acoating or a laminated dyeable film that is bonded to the inside oroutside of a plastic or glass lens 12. If the plastic or glass lens isphotochromic and the dyeable film is on the inside (concave) of the lensthe dyes will block the UV necessary to activate the photochromicmaterial before the UV enters the eye.

The synergistic effect of having a lens 12 with a polarizer 16 and acombination dye 18 that substantially absorbs blue light results in alens that provides effective protection to the retina. The idealsituation is to minimize the need for blue blocking, by staying belowthe damage-repair threshold, and eliminating the thermal heating of theretina by the glints of light that pass across the retina as discussedin the Disclosure of the Invention section. The inventive lens 10accomplishes this protection by blocking the horizontally polarizedglints of light in the blue and UV wavelengths.

The combination dye 18 available for use with the lens 12 can beselected to substantially block all wavelengths in the electromagneticspectrum between 300 and 549 nanometers. The specific cut-on wavelengthselected within this spectral range is dependent upon the comfort of theuser in a specific usage environment. The specific cut-on of the lensdepends upon the time, temperature, and component dyes used to make thecombination dye.

To process a lens 12, an optical plastic lens having a polarizing film16 embedded therein is procured. If a cut-on wavelength at 450nanometers is desired, a combination dye 18 is applied to lens 12 by ahot-dip combination dispersed dye process. The process essentiallyconsists of immersing the lens into a vessel containing a mixture ofdispersed yellow twenty-three dye 24 and a dispersed orange three dye 20in a concentration ratio of approximately 1 to 1. The lens 12 remains inthe vessel for a period of 2.5 minutes at a temperature of 98±1 degreecentigrade.

If a cut-on wavelength at 500 nanometers is desired, the lens 12 isimmersed into a vessel containing a mixture of dispersed yellowtwenty-three dye 24 and a dispersed orange three dye 20 in aconcentration ratio of approximately 1 to 1 for a period of 5.0 minutesat a temperature of 98±1 degrees centigrade.

For a cut-on wavelength at 515 nanometers, the lens 12 is immersed intoa vessel containing a mixture of dispersed yellow twenty-three dye 24and a dispersed orange three dye 20 in a concentration ratio ofapproximately 1 to 1 for a period of 12.0 minutes at a temperature of98±1 degrees centigrade.

For a cut-on wavelength at 530 nanometers, the lens 12 is immersed intoa vessel containing a mixture of dispersed red two dye and a dispersedorange three dye 20 in a concentration ratio of approximately 1 to 1 fora period of 4.5 minutes at a temperature of 98±1 degrees centigrade.

For a cut-on wavelength at 550 nanometers, the lens 12 is immersed intoa vessel containing a mixture of dispersed red two dye and a dispersedorange three dye 20 in a concentration ratio of approximately 1 to 1 fora period of 12.0 minutes at a temperature of 98±1 degrees centigrade.

The best mode process for preparing the lens 12 is the hot-dipcombination dispersed dye process described supra. Other processes thatmay also be used to apply the combination dye 18 or individual dyesinclude a laminate film process, a solvent dyed coating process, acold-dip solvent-dye process and a pre-solvent-dyed molded-plasticprocess. The additional processes are well known in the art and aretherefore not described.

The processes that use the combination dye 18 may be used for all thesharp cut-on filters 14 described earlier. For filters that cut-onbetween 450 and 530 a single orange or red hot-dip dye may be used withspecial heat resistant polarizing lenses.

In this alternative process, if a cut-on at 450 nanometers is desired,the lens 12 is immersed into a vessel containing the yellow twenty-threedye 24 for a period of 16 minutes at a temperature of 98±1 degreesCentigrade.

For a cut-on at 500 nanometers, the lens 12 is immersed into a vesselcontaining the orange three dye 20 for a period of 5 minutes at atemperature of 98±1 degrees Centigrade.

For a cut-on at 515 nanometers, the lens 12 is immersed into a vesselcontaining the orange three dye 20 for a period of 12 minutes at atemperature of 98±1 degrees Centigrade.

For a cut-on at 530 nanometers, the lens 12 is immersed into a vesselcontaining the orange three dye 20 for a period of 18 minutes at atemperature of 98±1 degrees Centigrade.

For a cut-on at 550 nanometers, the lens 12 is immersed into a vesselcontaining the red two dye for a period of 18 minutes at a temperatureof 98±1 degrees Centigrade.

The standard temperature of 98±1 degree as used in the preferred processmay be changed to 37±1 degrees Centigrade. When the lens 12 is immersedat this lower temperature, the time required is about 7 to 10 days.

The combination dye 18 selected for use with the lens 12 is dependentupon its ultimate use. All reasonable viewing problems can be solved byusing a polarized lens incorporating sharp cut-on filter 14. Fivetypical problem situations are considered: a lifeguard, a boater, afisherman, a driver, and a pilot--the hazard weighted irradiancereferred to in the discussion as well as other numerical and technicalnotations are derived and described in the Disclosure of the Inventionsection. The spectra of these lenses are shown in FIG. 1.

The typical situation for the lifeguard is as follows: The time is noon,with the sun at zenith. The lifeguard is 8 meters away from the waterwhich has waves on it with a radius of curvature of 3 meters. The hazardweighted irradiance is 3.27 microW/cm² which is far above the thresholdfor both solar retinitis and night vision loss. With a 500 cut-onfilter, the irradiance drops to 0.036 microW/cm² which is below thethreshold for solar retinitis but above the threshold for night visionloss. With the addition of the polarizer, the hazard weighted irradianceis reduced to 0.004 microW/cm² which is below the night vision lossthreshold.

The typical situation for the boater is as follows: The time is noon,with the sun at zenith. The boater is 4.5 meters away from the waterwhich has waves on it with a radius of curvature of 3 meters. The hazardweighted irradiance is 8.20 microW/cm² which is far above the thresholdfor both solar retinitis and night vision loss. With a 515 cut-onfilter, the irradiance drops to 0.063 microW/cm² which is below thethreshold for solar retinitis but above the threshold for night visionloss. With the addition of the polarizer, the hazard weighted irradianceis reduced to 0.007 microW/cm² which is below the night vision lossthreshold.

The typical situation for the driver is as follows: The time is noon,with the sun at zenith. The driver is 5 meters away from the glasswindow of the car in front of it. The glass window has a radius ofcurvature of 4 meters. The hazard weighted irradiance is 39.60microW/cm² which is far above the threshold for both solar retinitis andnight vision loss. With a 530 cut-on filter, the irradiance drops to0.24 microW/cm² which is slightly above the threshold for solarretinitis and far above the threshold for night vision loss. With theaddition of the polarizer, the hazard weighted irradiance is reduced to0.002 microW/cm² which is below the night vision loss threshold.

The typical situation for the fisherman is as follows: The time is noon,with the sun at zenith. The fisherman is 6 meters away from the waterwhich has low waves on it with a radius of curvature of 6 meters. Thehazard weighted irradiance is 8.20 microW/cm² which is far above thethreshold for both solar retinitis and night vision loss. With a 550cut-on filter, the irradiance drops to 0.045 microW/cm² which is belowthe threshold for solar retinitis but above the threshold for nightvision loss. With the addition of the polarizer, the hazard weightedirradiance is reduced to 0.005 microW/cm² which is below the nightvision loss threshold.

The most protective filter is the 550 cut-on. The 550 cut-on wasselected as a limit because it is the greatest cut-on which does notinterfere with red-green-yellow color discrimination which is needed forsafety with traffic signals. This traffic signal recognition wasdetermined experimentally. This lens is the one of choice for personsrequiring the maximum protection such as those with diseased retinasi.e. Retinitis Pigmentosa, age-related macular degeneration etc.However, the lens may also be worn by others seeking maximum protection.

The typical situation for the police officer is as follows: The time isnoon, with the sun at zenith. The driver is 5 meters away from the glasswindow of the car in front of it. The glass window has a radius ofcurvature of 4 meters. The hazard weighted irradiance is 39.60microW/cm² which is far above the threshold for both solar retinitis andnight vision loss. With a 450 cut-on filter, the irradiance dropssomewhat, but because of the need for color verity by the officer tocorrectly identify the color of vehicles, the officer is above thresholdfor both the night vision loss threshold and the solar retinitisthreshold. However, he is still better off than if he did utilize thepolarizing blue blocking lens.

The typical situation for the pilot is as follows: The time is noon,with the sun at zenith. The pilot is a highly variable distance fromcloud cover which can change on short notice from overcast to brilliantsun. The state of polarization can also change dramatically dependingupon the direction of the sun and the could directions. For thesereasons it is difficult to predict the hazard the pilot is exposed to.However, it is known that the pilot is exposed to far more intensity ofoverall blue and UV due to the altitude. (Atmosphere absorbs UV and bluelight to some extent so persons at high altitude are at greater riskthan those close to sea level.) A pilot may be any cut-on lens from 515to 550 to mitigate the damage. The unexplained effect of this inventionwhich allows them to be used over a wide range of light conditions willbe of use to the pilot.

In general, for situations where the usage environment is well known anddefined, the suggested cut-on can be determined by the quantitativemethods described by equations [22] and [23]. In those situations wherethe usage environment is ill defined or highly variable, the suggestedcut-on can be determined by the comfort of the user in a specific usageenvironment.

While the invention has been described in complete detail andpictorially shown in the accompanying drawings it is not to be limitedto such details, since many changes and modification may be made to theinvention without departing from the spirit and the scope thereof. Forexample, the inventive lens 10 also has application in automobile andaircraft windshields, special application windows, flight, ski andwelding goggles or visors, and in microscopes, telescopes orophthalmoscopes. Hence, it is described to cover any and allmodifications and forms which may come within the language and scope ofthe claims.

We claim:
 1. A sunglass lens comprising:(a) means to substantially blockwavelengths in the electromagnetic spectrum that are between 300nanometers and a specific sharp cut-on wavelength that is selectedbetween a range of 450 and 550 nanometers, where the selection of thespecific cut-on wavelength is based on a trade-off between visibilityand safety that is determined quantitatively, (b) means to substantiallytransmit wavelengths in the visible portion of the electromagneticspectrum that are longer than 625 nanometers, and (c) means tosubstantially block horizontally polarized light.
 2. The sunglass lensas specified in claim 1 wherein the selection of the specific cut-onwavelength, that is based on a trade-off between visibility and safety,is determined quantitatively by application of the followingformulas:for point sources: ##EQU10## where: E_(bpolfiltered) =the totalcorneal irradiance, in Watts/cm², which results after the incident lighthas passed through the spectrally selective filter and the polarizer;E_(vertical) (I)=the unfiltered corneal spectral irradiance ofvertically polarized light caused by an image of the sun in W/(cm² *nm);T_(filter) (I)=the spectral transmission of the sunglass filter withoutpolarization; BLH(I)=the blue light hazard function as a function ofwavelength; ΔI=the interval of wavelength at which measurements aretaken and the calculation is made; I_(cut-on) wavelength =the cut-onwavelength best suited to the usage environment described byE_(vertical) (I); for extended sources: ##EQU11## where:L_(bpolfiltered) =the total corneal radiance, in Watt/(cm² *sr), whichresults after the incident light has passed through the spectrallyselective filter and the polarizer; L_(vertical) (I)=the unfilteredcorneal spectral radiance of vertically polarized light caused by animage of the sun in Watt/(cm² *sr*nm); T_(filter) (I)=the spectraltransmission of the sunglass filter without polarization; BLH(I)=theblue light hazard function as a function of wavelength; ΔI=the intervalof wavelength at which measurements are taken and the calculation ismade; I_(cut-on) wavelength =the cut-on wavelength best suited to theusage environment described by L_(vertical) (I).
 3. The sunglass lens asspecified in claim 1 wherein said means to substantially blockwavelengths between 300 nanometers and a specific sharp cut-onwavelength of 450 nanometers, to transmit between 10 and 90 percent ofthe wavelengths longer than 625 nanometers and to substantially blockhorizontally polarized light, is accomplished by incorporating into saidlens a polarized sharp cut-on filter that cuts-on at 450 nanometers. 4.The sunglass lens as specified in claim 1 wherein said means tosubstantially block wavelengths between 300 nanometers and a specificsharp cut-on wavelength of 500 nanometers, to transmit between 10 and 90percent of the wavelengths longer than 625 nanometers and tosubstantially block horizontally polarized light, is accomplished byincorporating into said lens a polarized sharp cut-on filter thatcuts-on at 500 nanometers.
 5. The sunglass lens as specified in claim 1wherein said means to substantially block wavelengths between 300nanometers and a specific sharp cut-on wavelength of 515 nanometers, totransmit between 10 and 90 percent of the wavelengths longer than 625nanometers and to substantially block horizontally polarized light, isaccomplished by incorporating into said lens a polarized sharp cut-onfilter that cuts-on at 515 nanometers.
 6. A sunglass lens as specifiedin claim 1 wherein said means to substantially block wavelengths between300 nanometers and a specific sharp cut-on wavelengths of 530nanometers, to transmit between 10 and 90 percent of the wavelengthslonger than 625 nanometers and to substantially block horizontallypolarized light, is accomplished by incorporating into said lens apolarized sharp cut-on filter that cuts-on at 530 nanometers.
 7. Thesunglass lens as specified in claim 1 wherein said means tosubstantially block wavelengths between 300 nanometers and a specificsharp cut-on wavelength of 550 nanometers, to transmit between 10 and 90percent of the wavelengths longer than 625 nanometers and tosubstantially block horizontally polarized light, is accomplished byincorporating into said lens a polarized sharp cut-on filter thatcuts-on at 550 nanometers.
 8. The sunglass lens as specified in claims3, 4 or 5 wherein said sharp cut-on filter that cuts-on at 450, 500 or515 nanometers is incorporated into said lens by applying to said lens acombination dye derived from a mixture of a yellow dye and an orangedye.
 9. The sunglass lens as specified in claims 6 or 7 wherein saidsharp cut-on filter that cuts-on at 530 to 550 nanometers isincorporated into said lens by applying to said lens a combination dyederived from a mixture of an orange dye and a red dye.
 10. The sunglasslens as specified in claims 3, 4, 5 or 6 wherein said sharp cut-onfilter that cuts-on at 450, 500, 515 or 530 nanometers is incorporatedinto said lens by applying to said lens an orange dye.
 11. The sunglasslens as specified in claim 1 wherein said means to block horizontallypolarized light is accomplished by a horizontally polarizing filter thatis applied to said lens by an application means.
 12. The sunglass lensas specified in claim 11 wherein said polarizing filter applicationmeans is accomplished by laminating a polarizing film into said lens.13. The sunglass lens as specified in claim 1 wherein said lens is madefrom optical plastic.
 14. The sunglass lens as specified in claim 13wherein said optical plastic is comprised of di-allyl glycol carbonate.15. The sunglass lens as specified in claim 1 wherein said lens is madefrom optical glass.
 16. The sunglass lens as specified in claim 11wherein said polarizing filter application means is accomplished bymolding a polarizing film into said lens.
 17. The sunglass lens asspecified in claim 12 wherein said polarizing film is dyed prior tolaminating said polarizing film.
 18. The sunglass lens as specified inclaim 16 wherein said polarizing film is dyed prior to molding saidpolarizing film.
 19. The sunglass lens as specified in claims 8 or 9further comprising a heat-resisting polarizing film to which said dye isapplied by an application means prior to laminating said film.